Highly Co2-Permeable And Selective Polymer Blend Membrane And Process For Preparing The Same

ABSTRACT

A polymer blend membrane includes a polyether-based copolymer and a polyether polymerized in situ and has high permeability and high selectivity for carbon dioxide. In the polymer blend membrane, the free volume of the polyether-based copolymer is greatly increased, and the adsorption capacity for carbon dioxide is enhanced. Thus, it can have excellent mechanical properties and excellent permeability and selectivity for carbon dioxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 17/735,148 filed May 3, 2022, which claims priority to KoreanPatent Application Nos. 10-2021-0058846, filed on May 6, 2021, and10-2022-0048287, filed on Apr. 19, 2022, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the contents of which in their entiretyare herein incorporated by reference.

BACKGROUND 1. Field

The present invention relates to a polymer blend membrane having highpermeability and high selectivity for CO₂ and to a process for preparingthe same. More specifically, the present invention relates to a polymerblend membrane having high permeability and high selectivity for carbondioxide, in which the formation of a polyether polymer having aspherical micellar structure is induced in a polyether-based copolymermatrix by applying heat to a mixed solution composed of apolyether-based copolymer, a polyether oligomer, and an initiator in apolymerization reactor, and to a process for preparing the same.

This work was supported by C1 Gas Refinery Program through the NationalResearch Foundation of Korea (NRF) funded by the Ministry of Science andICT (Project No. 2019M3D3A1A01069101) and Korea Institute of EnergyTechnology Evaluation and Planning (KETEP) grant funded by the Koreagovernment (MOTIE) (20212010200110, Development of compact CO₂ capturetechnology for combustion exhaust gas of urban LNG power plant).

2. Description of the Related Art

Efforts to reduce CO₂, which has a significant impact on global warming,are continuously being made. A gas separation membrane technology isbeing used for the separation and purification of carbon dioxide, andmembranes using various polymers are being developed. However,conventional polymer membranes have a conflicting relationship betweenpermeability and selectivity. As a result, there is a limit to theseparation performance that is recognized as an upper bound for variousseparation target gases such as CO₂/N₂ and CO₂/CH₄ (see J. Membr. Sci,2008, 320, 390-400).

In order to enhance the CO₂ separation performance, membranes using apolymer material containing ethylene oxide, which has a good affinitywith CO₂ by a dipole-quadrupole interaction, have been activelydeveloped. Polyethylene oxide (PEO)-based polymers, which are a kind ofpolyether, have a problem of low permeability due to their highcrystallinity, and polyethylene glycol (PEG), which is a low molecularweight of PEO, has a disadvantage in that it has weak mechanicalstrength. To solve this problem, studies on introducing PEG into blockcopolymers containing PEG, crosslinked polymers, polymeric blends, andinorganic materials have been conducted (see Macromolecules, 2004, 37,4590-4597, J. Membr. Sci, 2009, 339, 177-183, Science, 2006, 311,639-642).

Meanwhile, polymer blends are attracting a lot of attention as a verypractical method because the advantages of each polymer can be achievedthrough a simple preparation process. When a low-molecular-weight of PEGis mixed with the matrix of a PEG-blend membrane, the fractional freevolume (FFV) of the polymer matrix is increased, so that the gaspermeability can be enhanced. However, if PEG is introduced in an excess(e.g., 50% or more) into the polymer matrix, the mechanical propertiesof the membrane are significantly deteriorated. Accordingly, there is ademand for the development of a polymer blend membrane having excellentmechanical properties and gas permeability even when polyethylene glycolis introduced in a high content into the polymer matrix.

SUMMARY Technical Problem to be Solved

An object of the present invention is to provide a polymer blendmembrane having excellent mechanical properties and gas permeabilityeven when polyethylene glycol is introduced in a high content into thepolymer matrix.

Another object of the present invention is to provide a process forpreparing a polymer blend membrane having excellent mechanicalproperties and gas permeability even when polyethylene glycol isintroduced in a high content into the polymer matrix.

Solution to the Problem

According to an embodiment of the present invention, there is provided apolymer blend membrane, which comprises, based on the total weight ofcomponents (A) and (B), (A) 30 to 90% by weight of a polyether-basedcopolymer; and (B) 10 to 70% by weight of a polyether.

According to another embodiment of the present invention, there isprovided a process for preparing a polymer blend membrane, whichcomprises (1) dissolving a polyether-based copolymer resin; a polyetheroligomer containing a vinyl group; and an initiator in a solvent; (2)subjecting the polyether oligomer containing a vinyl group to in-situradical polymerization; and (3) molding the product obtained in step (2)in the form of a membrane and removing the solvent therefrom.

Advantageous Effects of the Invention

In the polymer blend membrane according to an embodiment of the presentinvention, the free volume of the polyether-based copolymer is greatlyincreased, and the CO₂ sorption capacity is enhanced. Thus, it can haveexcellent permeability and selectivity for carbon dioxide and durablemechanical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a membrane prepared according to anembodiment of the present invention.

FIGS. 2(a) and (b) show a nuclear magnetic resonance (¹H-NMR) spectrumof a polymer membrane prepared according to an embodiment of the presentinvention.

FIGS. 3(a)-(c) are graphs showing a Fourier-transform infraredspectroscopy (FT-IR) result of a polymer membrane prepared according toan embodiment of the present invention.

FIGS. 4(a) and (b) show an X-ray diffraction (XRD) spectrum of a polymermembrane prepared according to an embodiment of the present invention.

FIGS. 5(a) and (b) are graphs showing the fractional free volume anddensity of a polymer membrane prepared according to an embodiment of thepresent invention.

FIGS. 6(a) and (b) are graphs showing a differential scanningcalorimetry (DSC) result of a polymer membrane prepared according to anembodiment of the present invention.

FIG. 7 is a graph showing Young's modulus and hardness of a polymermembrane prepared according to an embodiment of the present invention.

FIGS. 8(a)-(f) show a transmission electron microscopy (TEM) image of apolymer membrane prepared according to an embodiment of the presentinvention.

FIGS. 9(a)-(d) are graphs showing the gas permeability and selectivityunder a single gas condition of a polymer membrane prepared according toan embodiment of the present invention.

FIGS. 10(a)-(d) show adsorption isotherms for CO₂ and CH₄ of a polymermembrane prepared according to an embodiment of the present invention.

FIGS. 11(a)-(c) are graphs showing the gas separation performance of apolymer membrane prepared according to an embodiment of the presentinvention in terms of the upper bound of polymers.

FIGS. 12(a) and (b) are graphs showing the mixed gas permeability andselectivity of a polymer membrane prepared according to an embodiment ofthe present invention.

DETAILED DESCRIPTION

Hereinafter, the present invention is explained in more detail.

Polymer Blend Membrane

According to an embodiment of the present invention, there is provided apolymer blend membrane, which comprises, based on the total weight ofcomponents (A) and (B), (A) 30 to 90% by weight of a polyether-basedcopolymer; and (B) 10 to 70% by weight of a polyether.

The polymer blend membrane according to an embodiment of the presentinvention comprises a polyether-based copolymer (A). Here, thepolyether-based copolymer (A) serves as a matrix.

In a specific embodiment of the present invention, the polyether-basedcopolymer (A) may comprise at least one selected from the groupconsisting of poly(ether-amide) (PEA), poly(ethylene oxide) (PEO),polyethersulfone (PES), and poly(ether-imide) (PEI), but it is notparticularly limited thereto.

In a preferred embodiment of the present invention, the polyether-basedcopolymer (A) may comprise a poly(ether-amide).

Here, the poly(ether-amide) is prepared by a polycondensation reactionof a carboxylic acid polyamide and an alcohol-terminated polyether, andit may be represented by Formula 1 below.

HO—(CO-PA-CO—O-PE-O)_(n)—H  [Formula 1]

In Formula 1, PA represents a polyamide repeat unit, PE represents apolyether repeat unit, and n may be 10 to 20.

In a specific embodiment of the present invention, examples of thepolyamide repeat unit include nylon 6, nylon 46, nylon 66, nylon 610,nylon 11, nylon 12, and nylon 6/66, but it is not limited thereto.

In a specific embodiment of the present invention, examples of thepolyether repeat unit include polyethylene glycol (PEG), polypropyleneglycol (PPG), and poly(tetramethylene ether) glycol (PTMEG), but it isnot limited thereto.

In a specific embodiment of the present invention, the poly(ether-amide)may have a weight average molecular weight of 30,000 to 100,000 g/mole,preferably 40,000 to 60,000 g/mole, more preferably about 50,000 g/mole.

In a specific embodiment of the present invention, the poly(ether-amide)may have a density of 1.01 to 1.14 g/cm³.

In a specific embodiment of the present invention, the poly(ether-amide)may comprise 20 to 70% by weight of a polyamide repeat unit and 30 to80% by weight of a polyether repeat unit based on the total weightthereof.

In a preferred embodiment of the present invention, thepoly(ether-amide) may be Pebax® 1657 in which the polyamide repeat unitis nylon 6, and the polyether repeat unit is polyethylene glycol. Pebax®1657 may be represented by Formula 2 below in which the content of nylon6, which is a polyamide repeat unit, may be 40% by weight, and thecontent of polyethylene glycol, which is a polyether repeat unit, may be60% by weight.

In Formula 2, x may be 57 to 60, y may be 33 to 40, and n may be 10 to20.

In the polymer blend membrane according to an embodiment of the presentinvention, the content of the poly(ether-amide) may be 30 to 90% byweight based on the total weight of the poly(ether-amide) and thepolyether. If the content of the poly(ether-amide) is less than 30% byweight, the mechanical properties of the polymer blend membrane to beprepared may be deteriorated; thus, it may not be suitable as a gasseparation membrane. Meanwhile, if the content of poly(ether-amide)exceeds 90% by weight, the enhancement in permeability of carbon dioxideof the polymer blend membrane to be prepared may be insufficient.

The polymer blend membrane according to an embodiment of the presentinvention comprises a polyether (B). Here, the polyether (B) serves as adispersed phase.

In a specific embodiment of the present invention, the polyether (B) maybe prepared by in-situ radical polymerization of a polyether oligomercomprising a vinyl group.

In a specific embodiment of the present invention, the polyether (B) mayhave a weight average molecular weight of 200 to 1,500 g/mole and 4 to34 of a polyether repeat unit.

In a specific embodiment of the present invention, the polyetheroligomer containing a vinyl group may comprise at least one selectedfrom the group consisting of poly(ethylene glycol) methacrylate,poly(ethylene glycol) methyl ether methacrylate, and poly(propyleneglycol) methyl ether acrylate, but it is not particularly limitedthereto.

In a preferred embodiment of the present invention, the polyetheroligomer containing a vinyl group may comprise poly(ethylene glycol)methyl ether acrylate (PEGMEA) represented by Formula 3 below.

In Formula 3, n is an integer of 8 to 9, and the number averagemolecular weight (Mn) of PEGMEA may be about 480 g/mole.

In a specific embodiment of the present invention, the radicalpolymerization of the polyether oligomer containing a vinyl group may becarried out in the presence of an initiator. Examples of the initiatorinclude benzoyl peroxide (BPO), di-tert-butyl peroxide (DTAP), potassiumpersulfate (KPS), 2,2′-azobis(2-methylpropionitrile (AIBN), and4,4′-azobis-4-cyanopentanoic acid (ACVA), but it is not particularlylimited thereto.

In a preferred embodiment of the present invention, the polyether(PPEGMEA or poly(PEGMEA)) produced by radical polymerization of PEGMEAmay be represented by Formula 4 below.

In Formula 4, n may be 8 to 9, and m may be 4 to 112.

In the polymer blend membrane according to an embodiment of the presentinvention, the content of the polyether (B) may be 10 to 70% by weightbased on the total weight of the poly(ether-amide) and the polyether. Ifthe content of the polyether (B) exceeds 70% by weight, the mechanicalproperties of the polymer blend membrane to be prepared may bedeteriorated; thus, it may not be suitable as a gas separation membrane.Meanwhile, if the content of the polyether (B) is less than 10% byweight, the enhancement in permeability of carbon dioxide of the polymerblend membrane to be prepared may be insufficient.

In the polymer blend membrane according to an embodiment of the presentinvention, the polyether-based copolymer (A) serves as a matrix, and thepolyether (B) serves as a dispersed phase.

In general, it is known that if a high amount of a low-molecular-weightpolyether component is contained in a polymer matrix, the mechanicalproperties of the polymer blend membrane are deteriorated. In contrast,a low-molecular-weight polyether component is subjected to in-situradical polymerization to form a spherical micellar structure and thendispersed in the matrix of the polyether-based copolymer in anembodiment of the present invention; thus, a polymer blend withexcellent mechanical properties can be prepared.

Specifically, as shown in FIG. 1 , PPEGMEA forms a spherical micellarstructure through self-assembly in a mixture of ethanol and water. Insuch an event, as the molecular weight increases, a micellar structurecan be better formed to reduce the interfacial free energy between thehydrophobic backbone (—CH—CH₂—) and the hydrophilic water. Since thespherical micellar structure of PPEGMEA thus formed with a highmolecular weight remarkably increases the fractional free volume (FFV)of the Pebax® 1657 polymer matrix, it dramatically enhances the gaspermeability. In addition, PPEGMEA enhances the CO₂ sorption capacity,so that the high selectivity of the polymer blend membrane for carbondioxide can be maintained.

In a specific embodiment of the present invention, the polymer blendmembrane may be a flat plate type. In such an event, the polymer blendmembrane may have a thickness of 5 to 200 μm, preferably, a thickness of10 to 100 μm, 20 to 80 μm, 30 to 80 μm, or 5 to 150 μm.

Alternatively, the polymer blend membrane may be a hollow fibermembrane. The hollow fiber membrane may be prepared by, for example, adry-jet/wet-quench process. The hollow fiber membrane may have an outerdiameter of 200 to 1,000 μm and an inner diameter of 100 to 800 μm.Preferably, the hollow fiber membrane may have an outer diameter of 550to 650 μm and an inner diameter of 350 to 450 μm.

The polymer blend membrane according to an embodiment of the presentinvention can be advantageously used to separate carbon dioxide from amixed gas.

Process for Preparing a Polymer Blend Membrane

According to another embodiment of the present invention, there isprovided a process for preparing a polymer blend membrane, whichcomprises (1) dissolving a polyether-based copolymer resin; a polyetheroligomer containing a vinyl group; and an initiator in a solvent; (2)subjecting the polyether oligomer containing a vinyl group to in-situradical polymerization; and (3) molding the product obtained in step (2)in the form of a membrane and removing the solvent therefrom.

Step (1)

In step (1), a polyether-based copolymer resin; a polyether oligomercontaining a vinyl group; and an initiator are dissolved in a solvent.

Here, details on the polyether-based copolymer resin, the polyetheroligomer containing a vinyl group, and the initiator are as describedabove in the section of the polymer blend membrane.

The solvent is not particularly limited as long as the polyether-basedcopolymer resin; the polyether oligomer containing a vinyl group; andthe initiator can be dissolved therein. Preferably, examples of thesolvent include ethanol, water, N-methyl-2-pyrrolidone (NMP),dimethylformamide (DMF), dimethylacetamide (DMAc), and mixtures thereof,but it is not particularly limited thereto. In a specific embodiment ofthe present invention, the solvent may be a mixed solvent of ethanol andwater. In a preferred embodiment of the present invention, the solventmay be a mixed solvent of 70% by weight of ethanol and 30% by weight ofwater.

The sequence of dissolving the polyether-based copolymer resin; thepolyether oligomer containing a vinyl group; and the initiator is notparticularly limited. The polyether-based copolymer resin; the polyetheroligomer containing a vinyl group; and the initiator may be dissolved ina solvent in an arbitrary sequence. Alternatively, they may be dissolvedin a solvent at the same time. Once the polyether-based copolymer resin;the polyether oligomer containing a vinyl group; and the initiator havebeen added to a solvent, they are stirred at room temperature for about24 hours to be sufficiently dissolved.

In a specific embodiment of the present invention, the amount of thepolyether-based copolymer resin dissolved in a solvent may be 3 to 10%by weight. If the amount of the polyether-based copolymer resin exceeds10% by weight, it may be difficult to prepare a membrane since it may beeasily gelated at room temperature.

In a specific embodiment of the present invention, the amount of thepolyether oligomer containing a vinyl group may be 10 to 70% by weightbased on the total weight of the polyether-based copolymer resin and thepolyether oligomer containing a vinyl group dissolved in a solvent. Ifthe content of the polyether oligomer exceeds 70% by weight, themechanical properties of the polymer blend membrane to be prepared maybe deteriorated; thus, it may not be suitable as a gas separationmembrane. Meanwhile, if the content of the polyether oligomer is lessthan 10% by weight, the enhancement in permeability of carbon dioxide ofthe polymer blend membrane to be prepared may be insufficient.

In a specific embodiment of the present invention, the amount ofinitiator may be 0.5 to 3 moles per 100 moles of the polyether oligomercontaining a vinyl group dissolved in a solvent. If the content of theinitiator exceeds 3 moles, the micelle size of the polymerized polyetherpolymer is reduced; thus, it is difficult to effectively increase thedistance between the chains of the polymer matrix.

Step (2)

In step (2), the polyether oligomer comprising a vinyl group issubjected to in-situ radical polymerization.

The in-situ radical polymerization of the polyether oligomer containinga vinyl group may be carried out at a temperature of 60 to 80° C. for0.5 to 24 hours. Preferably, the in-situ radical polymerization of thepolyether oligomer may be carried out at a temperature of about 80° C.for about 24 hours.

The process for preparing a polymer blend membrane according to anembodiment of the present invention may further comprise removingbubbles from the product using an ultrasonicator after thepolymerization is completed.

Step (3)

In step (3), the product obtained in step (2) is molded in the form of amembrane, and the solvent is removed therefrom.

The method for molding the product obtained in step (2) in the form of amembrane is not particularly limited. As a specific example, the productobtained in step (2) is poured into a polystyrene petri dish and driedfor about 3 days to obtain a membrane. In such an event, in order tofacilitate evaporation of the solvent, it may be preferably furtherdried in a vacuum oven set at room temperature for 24 hours.

Gas Separation Method

According to another embodiment of the present invention, there isprovided a method for separating gases, which comprises passing a mixedgas containing at least carbon dioxide through the polymer blendmembrane according to an embodiment of the present invention to removeat least a portion of the carbon dioxide.

In a specific embodiment of the present invention, the method maycomprise separating at least one gas from a mixture of two or moregases. For example, the method may comprise separating carbon dioxidefrom a mixed gas comprising a combination selected from carbondioxide/nitrogen, carbon dioxide/carbon monoxide, carbon dioxide/oxygen,carbon dioxide/methane, carbon dioxide/hydrogen, and the like. But it isnot particularly limited thereto.

EXAMPLE

Hereinafter, the present invention will be described in more detail withreference to Examples and Comparative Examples. However, the followingexamples are for illustrative purposes only and are not intended tolimit the scope of the present invention.

The compounds used in the Examples and the Comparative Examples are asfollows.

-   -   poly(ether-amide) (Pebax 1657, Arkema)    -   polyether oligomer containing a vinyl group (PEGMEA, Sigma        Aldrich; molecular weight 480 g/mole)    -   benzoyl peroxide (BPO) initiator (Sigma Aldrich)

Comparative Example 1

Ethanol and water were mixed at a weight ratio of 70:30 to prepare asolvent. Pebax was added to the mixed solvent prepared above in anamount of 3% by weight and dissolved in an oil bath at 80° C. for oneday. Bubbles in the Pebax solution were removed using an ultrasonicator,and it was then poured into a polystyrene petri dish and dried at roomtemperature for 3 days. It was further dried in a vacuum oven at roomtemperature for one day to remove the residual solvent, therebypreparing a Pebax membrane.

Example 1

A 3% by weight Pebax solution was prepared in the same manner as inComparative Example 1. PEGMEA was added to the Pebax solution such thatthe weight ratio of Pebax:PEGMEA was 80:20, 50:50, and 30:70,respectively. Subsequently, BPO was added such that the molar ratio ofPEGMEA:BPO was 100:1. The solution thus obtained was stirred at roomtemperature for 2 hours. After all the components were dissolved,radical polymerization was carried out in an oil bath at 80° C. for 24hours. Upon completion of the polymerization, bubbles in the solutionwere removed using an ultrasonicator, and it was then poured into apolystyrene petri dish and dried at room temperature for 3 days. It wasfurther dried in a vacuum oven at room temperature for one day to removethe residual solvent, thereby preparing a Pebax/PPEGMEA_x(1) membrane.Here, x represents the initial weight ratio of PEGMEA to Pebax.

Example 2

Pebax/PPEGMEA_70 (y) membranes were prepared in the same manner as inExample 1, except that the weight ratio of Pebax:PEGMEA was 30:70 andthat the molar ratio of PEGMEA:BPO was adjusted to 100:1, 100:2, and100:3, respectively. Here, y represents the number of moles of BPO per100 moles of PEGMEA.

Comparative Example 2

A Pebax/PEGMEA_70 membrane was obtained in the same manner as inComparative Example 1, except that PEGMEA was added to the Pebaxsolution such that the weight ratio of Pebax:PEGMEA was 30:70.

Test Example 1

¹H-NMR analysis was performed to confirm the structure of the Pebax,PEGMEA, and Pebax/PPEGMEA membranes and the degree of polymerization ofPEGMEA, which is shown in FIGS. 2(a) and (b). The polyethylene oxide(PEO) group in Pebax appeared at 3.5-3.9 ppm (a), and the polyamide (PA)group appeared at 3-3.3 ppm (b), 2-2.6 ppm (c), and 1.8 ppm (d),respectively. The NMR peaks for PEGMEA appeared at 6-6.5 ppm (f, g),4-4.5 ppm (h), and 3.3-3.4 ppm (i), which correspond to vinyl,methylene, and methoxy groups, respectively. The Pebax/PPEGMEA membranesexhibited a new peak at 7.2-8 ppm (e) of benzene.

The conversion ratio of the vinyl group in PEGMEA was calculated throughthe relative area change of the vinyl group (f, g) based on the area ofthe methoxy peak (i). Specifically, the conversion ratio of the vinylgroup in PEGMEA was calculated by Equation 1 below.

Conversion (%)=(A _(i) −A _(fg))/A _(i)×100  [Equation 1]

Here, A_(i) is the peak area of the methoxy group, and A_(fg) is the sumof the peak areas of the vinyl group.

In all the Pebax/PPEGMEA membranes, the molecular weight of PPEGMEA wascalculated as the product of the repeat units of PPEGMEA and themolecular weight of PEGMEA. Here, the repeat unit was calculated fromthe peak areas of the benzene group as a terminal group of the initiatorand —CH—CH₂ as the main chain of PPEGMEA and the ratio of the number ofprotons thereof. Since the NMR peaks for the main chain (—CH—CH₂) ofPPEGMEA overlaps with those of the PA (—CH—CH₂) group in Pebax, thetheoretical number of —CH—CH₂ of PPEGMEA was calculated using the peakarea and proton number of the vinyl group. Specifically, the molecularweight of PPEGMEA was calculated by Equation 2 below.

Mn,_(NMR)=((3−A _(fg))/m _(fg))/(A _(e) /m _(e))  [Equation 2]

Here, A_(fg) is the sum of the peak areas of the vinyl group, A_(e) isthe peak area of the benzene group, m_(fg) is the number of protons inthe vinyl group, and m_(e) is the number of protons in the benzenegroup.

The theoretical molecular weight of PPEGMEA was calculated by Equation 3below.

Mn,_(theory)=(number of moles of PEGMEA)/(number of moles ofBPO)×(molecular weight of PEGMEA)×(conversion ratio of PEGMEA(%))+(molecular weight of BPO)  [Equation 3]

The conversion ratio of the vinyl group and the molecular weight ofPPEGMEA thus obtained are shown in Table 1 below.

TABLE 1 Pebax:PPEGMEA PPEGMEA:BPO Conversion Mn,_(NMR) Mn,_(theory)Sample (weight ratio) (molar ratio) (%) (g/mole) (g/mole)Pebax/PPEGMEA_20(1) 80:20 100:1 3.9 2,035 2,144 Pebax/PPEGMEA_50(1)50:50 100:1 70.6 47,067 34,130 Pebax/PPEGMEA_70(1) 30:70 100:1 94.353,905 45,522 Pebax/PPEGMEA_70(2) 30:70 100:2 96.8 35,188 23,466Pebax/PPEGMEA_70(3) 30:70 100:3 99.7 20,278 16,194

As the content of BPO increased from 1 mole to 3 moles inPebax/PPEGMEA_70 (y), the conversion of the vinyl group increased, whilethe molecular weight decreased. As the content of PEGMEA decreased from70% by weight to 20% by weight in Pebax/PPEGMEA_x(1), both theconversion and the molecular weight decreased. It was confirmed fromthese results that the theoretically calculated molecular weight(Mn,_(theory)) and the molecular weight obtained by ¹H-NMR were similar.

Test Example 2

FT-IR analysis of the Pebax and Pebax/PPEGMEA membranes was performed,and the results are shown in FIGS. 3(a)-(c). In the Pebax membrane, thehydrogen-bonded —NH group (stretching vibration) and the hydrogen-bonded—C═O group (stretching vibration) of PA appeared at 3,296 cm⁻¹ and 1,637cm⁻¹, respectively, and the hydrogen-bonded —C═O groups (stretchingvibration) and the hydrogen-bonded C—O—C groups (stretching vibration)of PEO appeared at 1,730 cm⁻¹ and 1,100 cm⁻¹, respectively. The samepeaks were observed in all the Pebax/PPEGMEA membranes.

It was confirmed that the peak intensity of the C—O—C group increased ascompared with Pebax in all the membranes to which PPEGMEA had beenintroduced. This attributes to the fact that when PEGMEA containing 80%by weight of PEG was mixed with Pebax (60% by weight of PEG), arelatively higher concentration of PEG than Pebax was introduced. In thePA in Pebax, a crystalline structure was induced through hydrogenbonding between the —NH group and the —C═O group. In all thePebax/PPEGMEA membranes, the —C═O bond of PA moved to a higher frequencythan Pebax while the hydrogen bond was reduced. As a result, anamorphous region was formed by interfering with the formation of acrystalline structure between PAs.

Test Example 3

XRD analysis of the Pebax and Pebax/PPEGMEA membranes was performed, andthe results are shown in FIGS. 4(a) and (b). An amorphous regionappeared in a wide region between a diffraction angle (2-theta) of 15°to 25°, and a strong peak appeared at 23.8°, which indicates acrystalline region of the polymer. The d-spacing values for theamorphous region are shown in Table 2. As the content of PEGMEA(x)increased from 20% to 70% by weight in Pebax/PPEGMEA_x(y), the d-spacingincreased from 4.24 Å to 4.30 Å as compared with Pebax. In addition, asBPO(y) increased from 1 mole to 3 moles, it decreased slightly from 4.30Å to 4.27 Å.

TABLE 2 Sample d-spacing(Å) Pebax 4.20 Pebax/PPEGMEA_20(1) 4.24Pebax/PPEGMEA_50(1) 4.27 Pebax/PPEGMEA_70(1) 4.30 Pebax/PPEGMEA_70(2)4.28 Pebax/PPEGMEA_70(3) 4.27

Test Example 4

To check the fractional free volume (FFV) of the prepared membranes, thedensities of all the membranes were measured, and FFV was calculatedtherefrom. The repeat units of PPEGMEA were calculated by ¹H-NMR. Asshown in FIGS. 5(a) and (b), the Pebax/PPEGMEA membranes showed a higherFFV than that of Pebax membrane, whereas their densities decreased. Asthe content of PEGMEA increased from 20% by weight to 70% by weight inPebax/PPEGMEA_x(1), the FFV increased and the density decreased. On theother hand, as the content of BPO increased from 1 mole to 3 moles inPebax/PPEGMEA_70 (y), the FFV decreased and the density increased. Here,Pebax/PPEGMEA_70 (1) had the highest FFV of 0.13.

Test Example 5

DSC analysis of the Pebax and Pebax/PPEGMEA membranes was performed forthe glass transition temperature (Tg) and the melting temperature (Tm)of PEG and PA, and the results are shown in FIGS. 6(a) and (b).

The Pebax membrane showed endothermic peaks of PEG and PA at 17° C. and206.2° C., respectively, and the Tg of PEG at −50.8° C. All thePebax/PPEGMEA membranes had a lower Tg than that of Pebax. When theinitiator was 1 mole, the Tg decreased from −56.1° C. to −60.6° C. asthe content of PPEGMEA increased from 20% by weight to 70% by weight. Inaddition, when the content of PEGMEA was 70% by weight, the Tg decreasedfrom −57.4° C. to −60.6° C. as the BPO decreased from 3 moles to 1 mole.It is understood that the reason that Tg decreased as compared withPebax is attributable to the fact that PPEGMEA increased the FFV ofPebax as an additive and increased the mobility of the polymer chains.

The crystallinity (Xc) of PEO or PA in the prepared membranes can becalculated through the ratio of the corresponding melting enthalpy(ΔH_(m)) and pure crystalline melting enthalpy (ΔH_(m) ⁰). These areshown in Table 3.

It is understood that in the Pebax/PPEGMEA membranes, the miscibility ofPPEGMEA with the Pebax matrix increased through an increase in Xc of PEGthan that of Pebax, and Xc increased by the entanglement between PPEGMEAand Pebax matrix through in-situ radical polymerization. On the otherhand, the Xc of PA decreased as the content of PEGMEA increased, and itdecreased as the content of the initiator increased at the same 70% byweight. As confirmed above, PPEGMEA reduced the crystallinity byinterfering with hydrogen bonding between the PA chains in Pebax.

TABLE 3 Xc (%) Sample Tg (° C.) PEG PA Pebax −50.8 21.81 11.98Pebax/PPEGMEA_20(1) −56.1 26.71 11.83 Pebax/PPEGMEA_50(1) −58.6 33.847.87 Pebax/PPEGMEA_70(1) −60.6 35.29 4.10 Pebax/PPEGMEA_70(2) −57.931.12 3.81 Pebax/PPEGMEA_70(3) −57.4 27.03 3.14

Test Example 6

Since it is known that the mechanical properties decrease as alow-molecular-weight PEG is introduced into Pebax, the mechanicalproperties of the membranes with respect to the content of the initiatorwere measured for the membranes in which Pebax was blended with 70% byweight of PEGMEA. Specifically, Young's modulus and hardness weremeasured through nanoindentation, and the results are shown in FIG. 7 .

Pebax/PEGMEA_70 and all the Pebax/PPEGMEA membranes showed lower Young'smodulus and hardness than Pebax. It is understood that this isattributable to the fact that the PA region having excellent mechanicalproperties was relatively reduced from 40% of Pebax to 12% ofPebax/PPEGMEA_70. Despite the above, all the membranes in which PPEGMEAhad been introduced in an amount of 70% by weight showed relatively highYoung's modulus and hardness as compared with Pebax/PEGMEA_70 membrane.In particular, Pebax/PPEGMEA_70 (1) showed the highest values. It isunderstood that PPEGMEA formed by in-situ radical polymerization had ahigher molecular weight than that of PEGMEA, and the mechanicalproperties of the membranes were enhanced by the entanglement of PPEGMEAand the Pebax matrix.

Test Example 7

The morphology and structure of the prepared membranes were observedusing TEM, and the results are shown in FIGS. 8(a)-(f). Pebax of FIG.8(a) had a PEO region and a dark PA region, with a microphase-separationform. The PA region showed a lamellar structure and had a crystallinestructure.

A black spherical PPEGMEA was observed in the Pebax/PPEGMEA_70 (y)membranes (FIG. 8 (d-f)). In Pebax/PPEGMEA_20 (1) and Pebax/PPEGMEA_50(1), smaller spheres as indicated by arrows than the three types inPebax/PPEGMEA_70 (y) were observed. As can be seen from the ¹H-NMRanalysis above, it seems difficult to observe them in TEM because theconversion ratio of the vinyl group was lower than that ofPebax/PPEGMEA_70 (y), so that the content of PPEGMEA formed in the Pebaxpolymer matrix was low.

In Pebax/PPEGMEA_70 (y), as the content of BPO decreased, the conversionratio of vinyl groups decreased, whereas the molecular weight increased,thereby increasing the size of micellar PPEGMEA (FIG. 8 (d-f)). Inparticular, micellar PPEGMEA with a size of approximately 150 nm wasobserved in Pebax/PPEGMEA_70 (1). PEGMEA formed PPEGMEA (orpoly(PEGMEA)) through in-situ radical polymerization in an ethanol/watersolvent, showing a micellar structure through self-assembly.

The micellar-structured PPEGMEA is composed of a hydrophobic —CH₂—CH—(backbone) group and a hydrophilic PEG group. The hydrophobic groupsform a micellar structure to reduce interfacial free energy with water.As the molecular weight of PPEGMEA increases, its size increases due toaggregation between the PPEGMEA chains of the formed micelles. As thesize of micelles increases, they have a bulky structure, which caneffectively increase the distance between the chains of the Pebaxmatrix.

Test Example 8

The membranes prepared in the Examples were each measured for the gaspermeability of hydrogen (H₂), carbon dioxide (CO₂), oxygen (O₂),nitrogen (N₂), carbon monoxide (CO), and methane (CH₄). The results areshown in FIGS. 9(a)-(d) and Table 4. In addition, the selectivities forCO₂/H₂, CO₂/N₂, CO₂/O₂, CO₂/CO, and CO₂/CH₄ based thereon are shown inTable 5.

The Pebax/PEGMEA membrane in which 70% by weight of oligomeric PEGMEAhad been introduced had very poor mechanical properties, as confirmed bythe measurements of Young's modulus and hardness, so that it wasdifficult to measure the separation performance. In contrast, all thePebax/PPEGMEA membranes had enhanced permeability regardless of the gastype as compared with Pebax. As the content of PEGMEA increased or thecontent of BPO decreased, the gas permeability further increased. Thisconforms to the FFV trend as described above concerning FIGS. 5(a) and(b).

The CO₂ permeability in Pebax/PPEGMEA_70 (1) was 1,388.3±65 Barrer,which was increased by 1,054% as compared with the pristine Pebax.Although the permeability of CO₂ was significantly enhanced, theselectivity for CO₂/H₂, CO₂/N₂, CO₂/O₂, CO₂/CO, and CO₂/CH₄ was hardlychanged. It is understood that this is attributable to the fact that thesorption capacity for CO₂ was enhanced by the increased amount of PEGintroduced.

In all the membranes, the gas permeability decreased in the order ofCO₂>>>H₂>CH₄>O₂>CO>N₂. It is understood that the excellent permeabilitycharacteristics for CO₂ are attributable to the dipole-quadrupoleinteraction between PEG and CO₂. In addition, CH₄, which has a largerkinetic diameter than CO and N₂, had higher permeability due to therelatively high condensability of the rubbery polymer membrane.

TABLE 4 Permeability (Barrer) Sample CO₂ H₂ CH₄ O₂ CO N₂ Pebax 120.3 ±9.6 13.8 ± 0.5  7.9 ± 0.2  5.4 4.6 ± 0.6 2.7 ± 0.4 Pebax/PPEGMEA_20(1)308.4 29.9 22.1 15.1 11.3 6.8 Pebax/PPEGMEA_50(1) 424.7 38.3 30.8 24.116.3 9.4 Pebax/PPEGMEA_70(1) 1,388.3 ± 3.0  120.3 ± 4.0  96.9 ± 5.2 78.748.1 ± 3.02 29.8 ± 2.4  Pebax/PPEGMEA_70(2) 556.1 54.3 39.3 — 21.0 12.9 Pebax/PPEGMEA_70(3) 372.1 ± 1.0 36.3 ± 1.0 27.0 ± 2.6 — 13.8 ± 1.0  8.5± 0.6

TABLE 5 Selectivity (P_(i)/P_(j)) Sample CO₂/N₂ CO₂/CO CO₂/O₂ CO₂/CH₄CO₂/H₂ Pebax 44.9 ± 3.4 26.2 ± 1.4 19.7 15.2 ± 0.8  8.7 ± 0.4Pebax/PPEGMEA_20(1) 45.2 27.2 20.4 13.9 10.3 Pebax/PPEGMEA_50(1) 44.726.1 17.7 13.8 11.3 Pebax/PPEGMEA_70(1) 46.7 ± 0.6 28.8 ± 0.1 17.1 14.3± 0.2 11.6 ± 0.4 Pebax/PPEGMEA_70(2) 43.2 26.6 — 14.2 10.2Pebax/PPEGMEA_70(3) 43.6 ± 1.1 26.9 ± 0.8 — 13.8 ± 0.7 10.3 ± 0.2

In order to check the gas diffusion coefficient and sorption coefficientof the prepared membranes, a gas adsorption experiment for carbondioxide and methane was performed. The results are shown in FIGS.10(a)-(d). Since all the membranes are rubbery polymers, the adsorptionisotherms of both CO₂ and CH₄ followed Henry's law. As the content ofPEGMEA increased or the content of BPO decreased in the Pebax/PPEGMEAmembranes, the gas sorption uptake of carbon dioxide and methaneincreased.

The sorption coefficient and diffusion coefficient and the correspondingsolubility selectivity and diffusivity selectivity based on the aboveexperimental results are shown in Table 6. As the content of PEGMEAincreased or the content of BPO decreased, both the diffusioncoefficient and sorption coefficient of carbon dioxide and methaneincreased. As the content of PEGMEA in Pebax/PPEGMEA_x(1) increased, thechain mobility of the polymer membranes increased, enhancing thediffusion coefficient owing to the enhanced FFV. The FFV increased dueto the formation of bulky micellar structures as the content BPOdecreased in Pebax/PPEGMEA_70 (y).

The sorption coefficient of carbon dioxide increased as the content ofPPEGMEA increased in all the Pebax/PPEGMEA membranes as compared withPebax. As the content of PEGMEA increased or the content of BPOdecreased, the sorption selectivity increased, and a trade-offrelationship with lower diffusivity selectivity than Pebax in thePebax/PPEGMEA membranes was confirmed. Thus, it was confirmed that theideal selectivity for carbon dioxide/methane, which is the product of adiffusivity selectivity and solubility selectivity, was maintained.

It was confirmed through the above experimental results that the FFV andthe amorphous region increased by PPEGMEA as an additive, which enhancedthe gas permeation characteristics, and selective separation of CO₂ byPEG was possible.

TABLE 6 D^(a) S^(b) D_(i)/D_(j) S_(i)/S_(j) Sample CO₂ CH₄ CO₂ CH₄CO₂/CH₄ CO₂/CH₄ Pebax 1.10 ± 0.08 2.38 ± 0.08 109.69 ± 0.82  3.32 ± 0.040.46 ± 0.02 33.1 ± 0.2 Pebax/PPEGMEA_20(1) 1.65 4.08 187.49 5.42 0.4034.6 Pebax/PPEGMEA_50(1) 1.77 4.53 239.66 6.81 0.39 35.2Pebax/PPEGMEA_70(1) 5.45 ± 0.27 13.90 ± 1.20  255.32 ± 29.61 7.01 ± 0.980.39 ± 0.01 36.4 ± 0.9 Pebax/PPEGMEA_70(2) 2.44 6.09 227.93 6.45 0.4035.3 Pebax/PPEGMEA_70(3) 1.99 ± 0.27 4.99 ± 0.54 188.57 ± 16.93 5.43 ±0.42 0.40 ± 0.01 34.7 ± 0.4

FIGS. 11(a)-(c) shows the separation performance of the Pebax andPebax/PPEGMEA membranes for CO₂/H₂, CO₂/N₂, and CO₂/CH₄ as compared withthe reported upper bound of conventional polymer membranes. All thePebax/PPEGMEA membranes showed overall superior separation performanceas compared with the Pebax membrane. In particular, the Pebax/PPEGMEA_70(1) polymer blend membrane showed the best separation performance.

Test Example 9

The permeability behavior of the Pebax and Pebax/PPEGEMA_70 (y)membranes for a mixed gas of CO₂/N₂ (50:50 molar ratio) and CO₂/CH₄(50:50 molar ratio) was observed with a change in pressure. The resultsare shown in FIGS. 12(a) and (b).

Similar permeability to the single gas permeability results wasconfirmed in all the membranes at a CO₂ partial pressure of 1 atm. Inaddition, the separation factor for CO₂/CH₄ was 13.3-14.7, which was notsignificantly different from the gas permeation selectivity (13.8-15.2)under the single gas condition, whereas the separation factor for CO₂/N₂was reduced by 20% as compared with the gas permeation selectivity underthe single gas condition.

It is understood that CO₂ adsorbed on a polymer matrix causedplasticization of the matrix to enhance the permeability of N₂, which isa non-condensable gas. As the partial pressure of CO₂ increased from 1bar to 10 bar, the permeability of CO₂ increased and the selectivity ofCO₂/CH₄ and CO₂/N₂ decreased. A separation membrane prepared by simplymixing 50% by weight or more of a PEG-based monomer or oligomer in Pebaxhas been reported to have a sharp decrease in permeability at a pressureof 1 bar or more (see Sep. Purif. Technol, 2021, 261, 118243). Incontrast, in the Pebax/PPEGMEA_70 (y) membrane of the present invention,the gas permeability and selectivity remained almost constant over thepressure range from 1 to 10 bar (CO₂ partial pressure) despite 70% byweight of PPEGMEA being introduced. It can be seen from this result thatPPEGMEA introduced in a high content shows excellent separationperformance and durability.

What is claimed is:
 1. A process for preparing a polymer blend membrane,comprising: (1) dissolving a polyether-based copolymer resin, apolyether oligomer containing a vinyl group, and an initiator in asolvent; (2) subjecting the polyether oligomer containing a vinyl groupto in-situ radical polymerization; and (3) molding a product obtained instep (2) in the form of a membrane and removing the solvent therefrom.2. The process for preparing a polymer blend membrane of claim 1,wherein the polyether (B) has a weight average molecular weight of 200to 1,500 g/mole.
 3. The process for preparing a polymer blend membraneof claim 1, wherein the solvent comprises at least one of the groupconsisting of ethanol, water, N-methyl-2-pyrrolidone (NMP),dimethylformamide (DMF), dimethylacetamide (DMAc), and mixtures thereof.4. The process for preparing a polymer blend membrane of claim 3,wherein the solvent is a mixed solvent of 70% by weight of ethanol and30% by weight of water.
 5. The process for preparing a polymer blendmembrane of claim 1, wherein the initiator comprises at least one of thegroup consisting of benzoyl peroxide (BPO), di-tert-butyl peroxide(DTAP), potassium persulfate (KPS), 2,2′-azobis(2-methylpropionitrile(AIBN), and 4,4′-azobis-4-cyanopentanoic acid (ACVA).
 6. The process forpreparing a polymer blend membrane of claim 5, wherein the initiatorcomprises benzoyl peroxide (BPO).
 7. The process for preparing a polymerblend membrane of claim 1, wherein the in-situ radical polymerization ofthe polyether oligomer containing a vinyl group is carried out at atemperature of 60 to 80° C. for 0.5 to 24 hours.